Treatment of leaded brass alloys for improving machineability and products so produced



United States Patent Lewis E. Thelin, Waterbury, Conn., assignor to TheBristol Brass Corporation, Bristol, Conn., a corporation of ConnecticutNo Drawing.

8 Claims.

Filed July 5, 1962, Ser. No. 207,802

This invention relates to the treatment of copperbase alloys, and moreparticularly to the treatment of leaded brass, or free-cutting brass, toimprove machineability.

For many years, the leaded brass alloys in use have been considered asadequate for the machine tools in use. More recently, however, thedevelopment of machine tools with high peripheral and machine speedshave indicated deficiencies in the usefulness and adaptability of theavailable free-cutting brasses.

An important object of the invention therefore is to provide a leadedbrass alloy having improved qualities for machining purposes.

A further object is in the provision of a leaded brass which will reduceabrasion to toolfaces during machining operations therebyincreasing toollife and decreasing tool wear.

Broadly speaking, leaded brass is a lead-copper-zinc alloy consistingessentially of 6090% copper, 0.25- 4.0% lead, and the balance of zinc.The commercially most important brass within this range comprises 60-65% copper, 0.254.0% lead, and the remainder zinc. Operationscontemplated Within the purview of this invention are those such as areperformed in screw machines, drill presses, milling machines, turretlathes, embossers, and the like, and may include threading and knurling.

Of necessity, commercial brasses are made with a high proportion ofscrap and remelt. Therefore, it is usually quite difficult to controlthe specific proportions of impurities within the alloy while stillremaining within the A.S.T.M. standards of about .25% permissibleimpurities. Such elements as iron, tin, aluminium, nickel, cadmium,antimony, and silicon may be present in uncontrollable quantities. Theseimpurities, including complex lead-copper-zinc oxides and othercompounds, al-

though sub-microscopic in size, seriously affect the machineability ofleaded brasses. The impurities may exist on the surface or be disbursedthroughout more particularly on the lead particles. Since it is wellknown that the lead is added as a chip breaker, the impurities existingon the lead particles are detrimental to the machineability. Moreoverthe machineability of leaded brasses does not necessarily conform to thestandard properties, such as tensile strength, percent elongation, etc.Thus machineability cannot be adequately determined in this manner.

The present invention contemplates the use of very specific proportionsof certain elements added to the leaded brass, for example, calcium,lithium and magnesium. Apparently lithium is most effective, 'withcalcium next in effectiveness. The use of such metals has been known forthe casting of copper oxide scavenger for improving the pouring andcasting qualities. These additive metals usually substantially boil offin casting. Moreover, it has always been felt that the more added thebetter, with cost being the only consideration. Effectiveness of suchadditive elements as calcium-lithium, on cleaning lead when zinc ispresent, was unknown. Zinc itself has been acting as a scavenging agentfor the casting and whether the additive elements react with the zincand copper, and not the lead has been heretofore 3,298,828 Patented Jan.17, 1967 ice undetermined. Furthermore, before machining, the leadedbrass must undergo operations such as drawing to rod. The effect of suchoperations was not entirely clear, particularly since grain size anddistribution is affected.

The addition of these elements must be controlled very carefully to thetype of material being melted. Otherwise adverse properties will result.For example the present invention contemplates the use of a substantialportion of scrap. This is probably, but not necessarily, due to theformation of complex chemical compounds not removed before casting,which complex compounds, although sub-microscopic in size, seriouslyaffect tool wear by abrasion. Excessive use of the additive elemeritswould adversely affect machineability, as would insufficient use. Theexact reason for this is not readily determined, but the followingexamples provide some evidence. Distribution, quality, and size of thelead particles may be a factor, and excessive addition of these elementsmay cause too much cleaning in one area, thereby reducing uniformity andconsequently machineability. Moreover, for fine machining an excesswould seem to increase the tendency of undesirable firecracking. I

1 Example 1 A lot of free cutting brass billets for use as rod were castat 2100 using the following charges:

Pounds Leaded brass alloy'scrap 850 Copper- Zinc 82 Lead 8 The resultinganalysis showed 62.03% copper, 2.95% lead, 0.15% iron and otherimpurities, and the remainder zinc. Alpha-beta structure was present innormal proportion. The bil lets were extruded to round rod, drawn to0.406 round, annealed to between 8001100, and again drawn to 0.328"round The resulting rod was all Alpha structure with normal leaddistribution. The properties tested showed a tensile strength of 74,000p.s.i., yield strength of 61,000 p.s.i., 10% elongation in 2 inches,with a consequent 48.7% reduction of area. On a subsequent machiningoperation the rod ran 34 hours before the high speed steel toolsrequired sharpening to maintain the set machining depth. This was normalfor free cutting, or leaded, brass.

Example 2 A lot of billets was cast at 2l00 using proportions similar toExample 1, but before pouring the melt, calcium and lithium in equalproportions were added using a standard phosphorizer, at a ratio of 8ounces of calcium and lithium per 1000 lbs. of brass melt. The resultinganalysis showed 62.04% copper, 3.12% lead, 0.20% iron and the otherimpurities, and the remainder zinc. Again alpha-beta structure waspresent in apparently normal proportion. Extruding, drawing andannealing was conducted in the manner of Example 1 with the result beingall Alpha structure and apparently similar leaid distribution.Properties tested indicated 78,500 p.s.i. tensile strength, 61,200p.s.i. yield strength, 10% elongation in 2" with consequent 45.2%reduction. Machining operations indicated a shearing off and a tendencyto firecrack. The machine tools remained relatively sharp, since theshearing and firecracking were premature.

Example 3 The procedure according to Example 2 was followed except thatthe calcium lithium added was 2 ounces per 1000 pounds of leaded brass.Analysis disclosed a similar proportion of elements, with alpha-betastructure Q3 present. Preparation of rod-was as in the previousexamples, and resulted in all Alpha structure. Tested properties were73,500 p.s.i. tensile strength, 58,100 p.s.i. yield strength, 10%elongation in 2 inches with 46.9% area reduction. Results in machiningwere erratic, with some samples showing improved machineability andlonger tool life, while other samples gave results similar to Example 1.

Example 4 The procedure according to Example 2 was again followed exceptthat the calcium lithium ratio was 4 ounces per 1000 pounds melt. Asimilar proportion of elements again with alpha-beta structure presentin normal percentages. After processing to rod as in the previousexamples, apparently all Alpha structure was again the result.Properties were 70,600 p.s.i. tensile strength, 58,700 p.s.i. yieldstrength, 8.5% elongation in 2 inches with 41.1% area reduction.Machining was markedly improved, with tool life for the various samplesbeing at least one third longer, with some samples as much as 200percent longer. Neither shearing nor firecracking were evident, evenwith extremely thin walled machine parts.

Example Samples of the rod prepared in Example 4 were relief annealed at525 F. The mechanical properties were then 70,900 p.s.i. tensilestrength, 61,300 p.s.i. yield strength, 11% elongation in 2 inches, with44.4% area reduction. Results in machining were as good as EX- ample' 4,again with no firccracking in thinwalled parts.

By using a typical comparative drill test, the superiority of theintermediate range was confirmed. The test consisted of a horizontal /s"drill acting on the specimen, with the drill mounted on a track anddriven by a constant weight, the depth of drill in millimeters beingmeasured over a constant time.

Using a drilling time of 60 seconds, to compare Examples 1 and 2, thefollowing depth of drill resulted:

Example 1 (3 samples) A 4.5-5.0-50 Example 2 (3 samples) 4.54.0-4.0

This indicates relative superiority of no calciumlithium over the 8ounce ratio.

Using a drill time of 30 seconds to compare Examples 1, 4 and 5 Example1 3 samples) 2.0-2.0 2.s Example 4 (2 samples) 3.53.5 Example 5 (2samples) 3.0-3.0

4 Using a drill time of 30 seconds to compare Examples 1, 3 and 4.

Example 1 (3 samples) 3.03.0-3.5 Example 4 (3 samples) 3.S4.03.5 Example3 (3 samples) 4.53.02.5

Thus, example 4 exhibited regular superiority, while Example 3 waserratic, and suprisingly, Example 1 for drilling was superior to Example2.

Having thus described certain details of my invention, I claim:

1. A method of treating brass to improve the machineability thereofwhich comprises adding to molten brass an additive selected from thegroup consisting of lithium and admixtures of lithium and calcium in anamount of from two to eight ounces of additive per thousand pounds ofmolten brass.

2. A method according to claim 1 wherein the brass consists essentiallyof copper, lead and zinc.

3. A method according to claim 2 wherein the additive is a mixture ofequal parts by weight of lithium and calcium.

4. A method according to claim 2 wherein the additive is lithium.

5. Free-cutting brass having improved machining qualities containing anadditive selected from the group of lithium and admixtures of lithiumand calcium in an amount of from two to eight ounces of additive perthousand pounds of brass, said amount being determined by the additionof the said amount of additive to the brass when said brass is in amolten state.

6. Free-cutting brass according to claim 5 wherein the brass consistsessentially of copper, lead and zinc.

7. Free-cutting brass according to claim 6 wherein the additive is amixture of equal parts by weight of lithium and calcium.

8. Free-cutting brass according to claim 6 wherein the additive islithium.

References Cited by the Examiner UNITED STATES PATENTS 2,062,426 12/1936Pierson -157.5 2,169,188 3/1939 Kelly 75157.5 3,158,470 11/1964 Burgholfet al. 75-135 HYLAND BIZOT, Primary Examiner.

ROGER L. CAMPBELL, DAVID L. RECK,

Examiners.

D. L. REISDORF, R. O. DEAN, Assistant Examiners.

5. FREE-CUTTING BRASS HAVING IMPROVED MACHINING QUALITIES CONTAINING ANADDITIVE SELECTED FROM THE GROUP OF LITHIUM AND ADMIXTURES OF LITHIUMAND CALCIUM IN AN AMOUNT OF FROM TWO TO EIGHT OUNCES OF ADDITIVE PERTHOUSAND POUNDS OF BRASS, SAID AMOUNT BEING DETERMINED BY THE ADDITIONOF THE SAID AMOUNT OF ADDITIVE TO THE BRASS WHEN SAID BRASS IS IN AMOLTEN STATE.